Galvanized chain with a strength rating is all more or less the same as far as I know. PLEASE don't buy that high stregth low weight stuff. Just buy larger chain. The whole point is for it to be heavy. I would get a total of 50ft minimum to be really useful. And yes you can link the old peice to the new but there are better options than a shackle. Whatever you use make sure it won't ever come undone, you can cut it off if you need to.